In the given pentapeptide, find out an essential amino acid (Y) and the sequence present in the pentapeptide : [figure] Choose the correct answer from the options given below :
- arrayll(Y) & (Sequence) \ Serine & Thr-Ser-Asp-Ala-Gly array
- arrayll(Y) & (Sequence) \ Serine & Ser-Asp-Thr-Ala-Gly array
- arrayll(Y) & (Sequence) \ Threonine & Ser-Thr-Asp-Gly-Ala array
- arrayll(Y) & (Sequence) \ Threonine & Thr-Ser-Asp-Gly-Ala array
Answer
(4) arrayll(Y) & (Sequence) \ Threonine & Thr-Ser-Asp-Gly-Ala array
Solution
A peptide is written from the N-terminal (free -NH2) end to the C-terminal (free –COOH) end. Side chains on the α-carbons, from left to right:
1st: -CH(OH)CH3 Threonine (Thr)
2nd: -CH2OH Serine (Ser)
3rd: -CH2COOH Aspartic acid (Asp)
4th: –H Glycine (Gly)
5th: -CH3 Alanine (Ala)
Sequence: Thr-Ser-Asp-Gly-Ala
As per NCERT, threonine is an essential amino acid (it cannot be synthesised in the body), whereas serine, aspartic acid, glycine and alanine are non-essential.
Y = Threonine
Answer: (4)